1. Field of the Invention
This invention relates generally to a method for identifying performance characteristics of fuel injectors during vehicle engine operation, and more particularly, to a system and method for identifying and characterizing the flow rates of fuel injectors during a vehicle engine operation that occurs in real time and is self learning.
2. Discussion of the Related Art
Almost all vehicle engines currently in production use fuel injectors rather than carburetors. Fuel injectors can deliver individual quantities of fuel to each cylinder in an engine, and are conducive to real-time control systems. However, as demands on engine performance and fuel efficiency grow, it is becoming increasingly important to understand and precisely predict the amount of fuel that a fuel injector will deliver in each injector pulse or cycle. This is difficult to do with high precision, given the manufacturing tolerances and other variations that can exist from one individual injector to another. The need for precise prediction of injector performance is particularly important in advanced technology engines which operate on a Homogeneous Charge Compression Ignition (HCCI) cycle, dual-mode engines which operate on either a Spark Ignition or Homogeneous Charge Compression Ignition (SI/HCCI) cycle, and Diesel engines.
A typical characteristic curve for a fuel injector measures the amount of fuel that the injector will deliver as a function of the pulse width (time) of the injection. Such a characteristic curve can be established through laboratory testing for any given model of fuel injector, at any particular fuel rail pressure. However, in a four-cylinder engine, for example, where four of the same model fuel injectors are used, each injector will vary slightly from the nominal characteristic curve. These variations make it very difficult for an engine controller to precisely control the amount of fuel injected per cycle, thus resulting in excess fuel consumption, incomplete combustion, and other undesirable effects.
What is needed is a method to allow an engine controller to learn during real-time engine operation the performance characteristics of each individual fuel injector in the engine, and adaptively respond to changes in the operating environment. This capability would result in better control of fuel injection quantities, which would yield significant improvements in engine performance and efficiency. It could even enable large-scale usage of HCCI engines, which until now has not been possible because of the difficulties in controlling the combustion.